Metal treatment



Oct. 25,1938. u. c; TAlNTON 2,134,457 I METAL TREATMENT I Filed March 2,1957 2 sheets-sheet 2 E INVENTOR Q ATTORN 1o is'not limited to thetreatmentof ferrous metal. tank it in a heated condition.

' is My invention comprises the step of subjecting specific example ofmy invention, the wirepasses 25 method in which the article is used as acathode tration or this'being H2804. Here the wire in presenting thisinvention, a specific emiution of zinc sulphate and Sulphuric a d n 3045 in Figs. 1 and 2.

Patented Oct. 25, 1938 I v I UNITED STATE rm'mi. 'rnsan'r Urlyn CliftonTainton, lBaltore, Application March 2, 1937, no; izacsz 21 on. (oi.Zlid-Jiii) My invention relates to the treatment of metal, are.connected to electric current sources 26, 21 particularly for thecleaning of the surface thereand 28-, respectively, electrodes It, itand it of. The invention is especially eflective for re-= beingrespectively negative, positive, and negamoving rust,scale, carbon andslag from the tive, while electrodes M, 32 and it are respec g surfaceof iron and steel, and is particularly aptively positive, negative andpositive. Guide 5 plicable as a preliminary treatment to various rolls25 serve to conduct current to wire ii, the coating operations, such asgalvanizing, en'amelwire.'thus being rendered cathodic in tank; i3, ing,painting, electroplating or the like. 'The inanodic in tank it and againcathodic in tank it. mention, however, as will later more fully appear,Gas burners 2e are provided for maintaining s Parr-2n orrrcs 10 Thisapplication is a continuation-in-part of Tank it contains a fused hathof sodium hy my applications Serial No. 630,233 and Serial No. droxidethrough whichthe wire passes. Current 692,378, filed August 24, 1932,and October 6, is passed through the fused'bath to electrolyze 1933,respectively. it, the wire serving as the cathode. --In this thesurfaces of metals to the reducing action of a through the bath at sucha rate that each pormetal more eiectropositive than the metal beingftion thereof remains immersed in the fused bath treated. For example,when iron or steel is befor a period of about thirty Seconds and the ingtreated it may be subjected to the action oi rent density employed isbetween 100 and 200 20 sodium or calcium, which metals areconsideramperes per square foot of cathodic surface. .20 ably' moreelectropositive than iron; From t it the wire passes through wash Morespecifically, my invention comprises the Water in tank it to remove theadherent sodium subjection of the metal article to be treated tohydroxide, thence w 1 1; through an aqueous the action of a moreelectropositive metal by a solution of sulphuri acidin tank iii, theconcenin a bath comprising compounds of the more acts as the anode, thecurrent density employed electropositive metals, under" such conditionsbeing of the order of 100 amperes per square that the moreelectropositive metal is liberated foot or greater.

- at the suriace of the article. The wire next passes through an aqueoussobodiment thereof will first be described, followed tank it, the zincsulphate being in such an by illustrative modifications and an outlineof the amount as to give a zinc content of 7 grams per generalprinciples upon which it rests 100 cubic centimeters oi solution and thesul- Accordingly I shall first describe the cleaning phuric acid about20%. Here the wire acts as 35 of'steel or iron wire as a step in themanufacthe cathode, the current density being of the 35 ture ofelectroplated zinc coated wire. order oi 200 amperes-or greater persquare foot Referring to the drawings: of cathodic surface. Here thewire is electro- Fig. 1 is a diagrammatic elevation, more or plated withmm. For the anodic treatment in less'in section, of a system forcleaning and electank lathe se composition may be employed in troplatingthe wire; as that in the coating of plating tank it. 40 1 Fig. 2 is aplan view of the same; and The anodic treatment of the wire in tank isFig. 3 is a diagrammatic elevation of a wire may be eflected with anelectrolyte oi substancleaning tank ior'eflecting a modification of thetially the se composition as the plating eleccleaning process carriedout in the system shown trolyte in tank it. It is to be understood, oi

cou'rsathat the most significant constituent of Referring first to Figs.1 and 2, the wire it this electrolyte used in 5M: iii is the sulphuricis led continuously from reel it successively acid, through cleaningtank itwash tank M,,anodic The treatment in tank it isthe mostsignificant cleaning tank It, and electroplating tank it, to stage ofthe process so far as this particular to reel ii. Electrodes it, l9 and2t depend into case is concerned and no claim is made herein 5o tanksIt, and it which also contain electrodes to the treatments in tanks itand it.- This M, 22 and 23, respectively. The'wire runs over treatmentin tank It eflectively cleans the surguide rolls 24 mounted on thetanks, and over face of, the wire, fully removingthose obstacles guiderolis' 25 mounted at the ends of electrodes to effective coating offerrous metal. Moreov vg5] l8, l9 and 20, The electrodes of the severaltanks this treatment produces a fpassive" condition oi cathode surface.Most commonly the current is from 100 to 200 amperes per square foot ofcathode surface.

While wire has just been given asan example of an article which may beadvantageously treated by the process just described, it is evident thatmetal articles generally may be treated by the cathodic cleaningoperation in fused sodium hydroxide whether the articles are tobe fedcontinuously through the fused bath, as in the case of wire, or are tobe treated intermittently. Ob-

viously the application of the cathodic, fused bath treatment is notlimited to articles which are to be zinc coated as in the specificillustration just given. The method is applicable wherever it is desiredto obtain an effectively cleaned metal surface. This type of cleaning isespecially effective as a preparation of metal surfaces for subsequentcoating operations, whether electrolytic or otherwise, includingenameling and the like, but its application is as wide as the need foreffectively cleaned metal surfaces.

The cleaning effect produced by the process set forth above is due tothe reducing action of the elemental sodium on the compounds, such asoxides, on the surface of the iron or steel being treated, the sodiumbeing liberated in the elemental condition during electrolysis of thefused bath. The reducing action of the sodium on the iron and otheroxides is enhanced by the nascent state of the electrolyticallyseparated metal.

For the most effective results, the electrolysis of the fused sodiumhydroxide should be so carried outthat the elemental sodium liberateddoes not collect in sensible amounts, preferably not in visible amounts,upon the article being treated and which article-acts as cathode duringthe electrolysis'. To effect this result, I employ conditions duringelectrolysis such that the sodium as fast as-it is separated from thesodium hydroxide, in the elemental state, is dissolved by or diffusedinto the bath of sodium hydroxida and consequently does not gather orcollect upon the surface of the article acting as cathode.

Under such conditions the sodium acts in two ways upon the oxides andother compounds on the articles surface: firstly, the sod um actsreducingly at the instant of its liberation from the sodium hydroxide,that is, it acts in its nascent condition; and secondly, the article isbathed by a solution of sodium in sodium hydroxide which acts reducinglyupon any compounds on the articles surface.

If conditions were to be used which would cause the collection ofsensible amounts of sodium on the cathode, as is done in the knownprocesses for electrolytic recovery of metallic sodium, the action ofthe sodium upon the article being treated would not be so effective aswhen the procedure just outlined is followed. If sodium is deposited insensible amounts upon the cathode article, it is practically impossibleto get uniform reduction of the oxides and other compounds upon itsHowever, suflicient current den-- surface. The sodium collectsirregularly upon the cathode surface, appearing as globules here andthere, and as soon as a portion of the cathode surface receives a filmof sodium, the rate and depth of reduction in that portion isimmediately diminished because the collected sodium is not so effectivea reducing agent as nascent sodium or sodium in solution, and since thefilm protects the surface from the direct action of nascent anddissolved sodium. Moreover, the conditions necessary for depositingsodium in sensible amounts upon the cathode are such that the sodiumhydroxide surrounding the article being treated contains little, if any,sodium in solution. Consequently even those portions of the article'ssurface which are not covered by a film of sodium are not so quickly andeffectively subjected .to

the action of the sodium.

Another factor whichwould interfere with getting the best results, whensodium is deposited in sensible amounts upon the article, is that ofreoxidation. As just stated above, the s-dium tends to gather more orless irregularly upon the cathode surface. Elemental sodium rapidlyforms oxides when brought into the air, the oxides of sodium being verypowerful oxidizing agents. When a ferrous or other metal article, havingglobules of sodium upon its surface emerges from the fused bath, oxidesof sodium are quickly formed which immediately reoxidize portions of thearticles surface.

The most easily imposed conditions for efl'ecting the treatment withsodium without collecting sensible quantities of sodium on the surfaceof the article being treated is by control of the temperature of thefused bath of sodium hydroxide. I maintain this fused bath at atemperature above that at which sodium collects upon the cathode. Bykeeping the bath at temperatures more than 20 C. in excess of themelting point of sodium hydroxide, the sodium is prevented fromcollecting on the cathode. At such temperatures the liberated sodium,which does not act immediately upon the compounds on the cathodesurface, dissolves forthwith in the sodium hydroxide and thus thearticle being treated is surrounded with a highly reducing liquid whichis exceedingly effective in rapidly reducing the compounds which may beupon the surface.

PreferablyI employ the sodium hydroxide bath at a minimum temperature of350 'C., but, as implied above, I may go as low'as a temperature just inexcess of 20 above the melting point of the sodium hydroxide.Consequently I may use a temperature as low as just in excess of 338 C.in the case of pure sodium hydroxide. Since most commercial sodiumhydroxides are more or less impure, their melting points are lower thanthat of the pure hydroxide, ordinarily ranging from about 295 C. to 300C., consequently with these impure sodium hydroxides I may operate atsomewhat lower temperatures, if desirable, namely at temperatures whichare Just in excess of 315 to 320 C.

Thus far we have considered the minimum temperature at which the fusedbath of sodium hydroxide is used. It is frequently desirable to operateat fairly high temperatures and this may be successfully done. The fusedbath may combine the function of annealing the metal articles with thatof its cleaning action thereon. Steel wire, for example, is commonlyproduced by being "cold drawn which operation introduces more or lessstresses or strains. By operating the fused bath at a sufficientlyelevated temperature these conditions maybe entirely relieved. With thisadditional function of annealing, or for that matter any desired form ofheat treatment, the fused bath will be used at temperatures bestadaptedto the particular material and purpose involved.

High chromium steels, including the so-called stainless steels" such asthe well known 18-8" (18% chromium, and 8% nickel), are advantageouslytreated by my cleaning process. In treating these high chromium steelsit is usually well to employ temperatures of the order of 538 C.. I

A very important aspect of my invention relates j to the control ofconditions to avoid or nullify the disadvantage of reoxidation of thesurface of the metal being treated. I have discovered thateunlesscertain precautions are taken the metal" quickly oxidizes uponremoval-from the cleaning and deoxidizing bath. If, in the operation ofthe process given above as an example of my invention, the bath ofsodium hydroxide is maintained at a temperature substantially above 550C., the surface of the iron or steel becomes oxidized when it passesfrom the fused sodium hydroxide in tank l3 into the air. This conditioncan frequently be obviated by maintaining the fused bath of sodiumhydroxide at a temperature below 550 C., at500 C., for example. By usingthe cleaning bath at this temperature the oxidation of the treated metalis usually avoided by preventing at the outset the condition of thesteel surface which leads to oxidation. -As will be apparent'later inthis specification, it is feasible under, certain circumstances tooperate the fused cleaning bath at temperatures which normally renderthe metal easily oxidizable and then to subject the metal being treatedimmediately to conditions which will overcome the tendency to oxidize.

The causes of this ready oxidability of the metal after leaving thefused bath are somewhat obscure, but it appears that under certainconditions, as when the temperature of the bath is higher than aparticular temperature, (550 C. in

. the caseof NaOH), the metal while in the bath,

or possibly as it leaves the bath, becomes covered with active oxidizingagents. As long as the metal being treated is performing the function ofcathode these oxidizing agents are of no effect, but when the metalpasses into the atmosphere, theseoxidizing agents become "active. Idonot wish .to be limited in my patent protection by any particularexplanationof these phenomena.

' In carrying out the process above described, it

' may beuseful in some cases to employ temperatures'of the fused bath inexcess of 550 C. It may be desired, for example, to effect an annealingof wire in the fused bath at a temperature say of 600 'C. If such atemperature of the. fused bath is employed in tank 13 the surface of thewire will oxidize when it enters the air. The oxides on the surface,thus produced, however, are not so closely adherent as those whichnormally occur on ferrous surfaces andthey may easily be removed byarelatively mild pickling operation in an aqueous acid bath, such apickling operation being much more easily and inexpensively carried outthan if the metal had not previously been subjected to the fused bath,treatment. Of course, when the article, after'its' treatment in thesodiumhydroxide bath, is given a treatment such as the anodic treatmentillustrated' in Figs. 1 and 2, the oxides'are effectively 15 removed.

oxides by the anodic operation has a disadvantage in that to efiecttheir complete removal it is usually necessary to prolong the anodictreatment thus slowing up the entire process. Ac-

;cordingly when I employ such temperatures of the fused bath as producethe tendency to ready oxidability I find it advantageous to use someform of procedure which will nullify this tendency.

In Fig. 3 I show means for carrying out a process in which this tendencyis overcome. The cleaning tank contains a fused bath of sodiumhydroxide. Wire, for example, ii is fed continuously through this bath,passing under guide rods at at the entry and exit ends thereof and beingengaged at intervals within the bath by the lower portions of electrodes33 which, being negative, render the wire cathodic. Nickel anodes 34 areprovided at intervals along the length of the tank. The sodium hydroxidebath is divided into two portions by partition 35 which has an opening30 through which wire il passes.

il. Box 3'! is placed relatively near to partition 35. Cooling water isfed into box 31 through pipe 38 and passes out through pipe 39. The

liquid sodium hydroxide adjacent box 31 is cooled and .falls to thelower part of the tank, the

hotter hydroxide flowing in to take its place, a circulation of the bathto the right of the partition thus being produced as indicated by thearrows in Fig. 3. By these means the portion of the bath at the exit endof the tank is maintained at a considerably lower temperature than thatportion of the bath at the entry end to the left of the partition.-

In place of or in addition to the means just described for controllingthe temperature of the I a cooling box 31 is provided which is immersedexit end of the bath I may employ a type of centration of heatattheinput end and allows the temperature at the exit end to remaincon-' siderably lower. Thus in Fig. 3 I have shown stoppers 42 of sheetrefractory material placed over some of the openings 43 in the firebrick arch 44 over which the pot is mounted. By this "device theproportion of combustion gas which passes through the arch at the exitend is reduced and the temperature of the exit end of the pot is reducedaccordingly. 3

By thesemea'ns it is feasible to maintain the bath to the left of thepartition at a desired temperature above550 C., say 600 C. andtheportion to the right of the partition at a desired temperature less than550 C., say 500 C. It is possible to secure the combined annealing andcleaning in the higher temperature portion of the bath, and by passingthe wire or other metal article through the lower temperature portion toovercome to a very substantial degree the tendency of the metal toreoxidize. In other words while the treatment to the left of thepartition by itself would give the metal a tendency to .furnace forheating the pot which permits conoxidize if it were then removed fromthe bath the treatment to the right of the partition, at the lowertemperature, largely overcomes this tendency.

Other means for overcoming or nullifying the tendency to oxidation ofthe metal may be employed. Referring to Fig. 3, a box 40 is located nearthe exit end of tank 30 into which a pipe 4| discharges steam near thebottom. Near the top of box 40, on the side opposite the exit end of thetank, is an opening adapted to discharge a stream of steam across thesurface of the fused bath and also across the wire as it issues from thefused bath. Box 40 serves to catch any water in the liquid state whichmay be entrained by the steam and therefore the steam which issues fromthe box and passes across the wire and the fused bath is substantiallyfree from liquid water.

Treating the wire in this manner likewise obviates or nulliflesthe'tendency of the wire surface to reoxidize. I believe that thistendency of the metal to oxidize rapidly upon removal from the fusedbath is due to the presence of actively oxidizing substances upon itssurface. The H2O, furnished in the form of steam, is believed to combinewith these substances to render'them non-oxidizing. It is likely that athigh temperatures, temperatures'above 550 C., NaaO is formed in the bathwhich is carried away on the surface of the wire. When H2O is brought incontact with the NazO it combines therewith to reform NaOH thustransforming an active oxidizing agent into one which is practicallynon-oxidizing. However, as I have already indicated, I do not wish tolimit my protection by any theory as to what may occur.

The steam seems to have an action in addition to that which it directlyeffects upon the wire as it issues from the fused bath. It appears tomodify somewhat the character of the bath with which it contacts in-thatit adds a small amount of H20 to the bath which combines with theoxidizing materials therein and thereby renders the exit portion of thebath relatively free from the tendency to furnish actively'oxidizingmaterials to the wire or other metal article.

While the several modes of overcoming the tendency of the metal tooxidize above described may be used alternatively, they may be used inconjunction as shown in the figure.

In this connection it may be well to call attention to the agitation ofthe fused bath in the exit portion of the tank due to the circulation ofthis portion of the bath. I have discovered that agitation of the fusedbath serves to overcome the tendency of the metal to oxidize. Even inthe absence of means for cooling the exit portion of the bath and of thetreatment of the metal and bath with steam, the tendency to oxidationmay be substantially or even completely overcome if the fused bath issufiiciently agitated.

Other means for preventing the rapid oxidation of the metal as it leavesthe fused cleaning bath may be employed. The oxygen in the air appearsto be'a factor in the reoxidation of the metal as it leaves the fusedbath. By providing an atmosphere of a non-oxidizing gas, particularlyone having a reducing action, reoxidation is substantially or entirelyprevented.

Instead of working with the higher temperatures of the bath which givethe tendency to active oxidation, it is of course practicable to employthe lower temperatures and effect an annealing points.

pounds of the alkaline earth metal group including magnesium, those ofcalcium being economically advantageous. Hereafter, when referringgenerically to these various metals and their compounds, I shall usuallydesignate them as highly electropositive metals or compounds thereof.

Not only with sodium hydroxide but with other compounds of sodium aswell as compounds of the other metals of the alkali metal group themetals of the alkaline,earth group, I prefer to operate at temperaturessubstantially above their meltthese highly electropositive metals ismuch more effective if the operating temperature of the bath issubstantially in excess of the melting point of the compound or mixtureof compounds which is used. Ordinarily. the operating temperature of thebath should be in excess of twenty degrees above the melting point ofthe bath. By so proceeding, I find that I avoid the superficialreduction of compounds which may occur if lower temperatures are used,moreover the resulting reduced metal is much more easily detached thanif the lower temperatures were to be used.

By selection of the proper compound for the fused bath or by a mixtureof compounds, a wide variety of effects may be produced, thus enablingone to select the conditions most suitable for his particular materialand problem. For example, if lower temperatures of operation, than thosesecurable by the use of sodium hydroxide, are desired, such temperaturescan be obtained by the use of compounds of lower melting points, such,for example, as sodium nitrite, (fusing at 213 0.), either alone ormixed with sodium hydroxide. By the judicious mixing of various sodiumand potassium salts, as is well known, a rather wide range of fusionpoints may be secured.

It will be obvious to the electro-chemist that I find that the reducingaction of the working conditions must frequently be altered with achange in the character of the fused bath employed. If a chloride of ahighly electro-positive metal were to be used, for example, it would benecessary that the anodes used should be of some material resistant tothe action of chlorine.

Usually in carrying out my cleaning operation it is important tomaintain the fused bath relatively constant in composition or at leastto allow variations only within definite limits. If there is unduevariation in the composition of the fused bath the temperature will varyunduly; If, for

example, sodium hydroxide is used for the bath undue formation of sodiumcarbonate through absorption from the air of carbon dioxide will lead tosuch an elevation of the melting point of the bath as to give bathtemperatures too high for the most satisfactory operation of my process.Where, for instance, it is desired to operate the bath of sodiumhydroxide at a temperature below 550 C. to prevent the ready oxidabilityof the metal, it is necessary that means be provided to prevent theabsorption of such an amount of carbon dioxide as will raise the meltingpoint above the desired operating temperature. The

' of replenishment of the fused bath by the addii 2,134,457 carbonatecontent of the fused bath will of course depend upon the rate of removalof the mixture of sodium hydroxide andsodium carbonate upon the surfaceof the metal being treated, the rate cover 50, the edges of which restin a lime seal disposed in trough 52 which surrounds the tank. Thiscover is provided with openings 53 through which wire ii passes into andout of the tank. Cover 50 is also provided with doors 54 through whicheasy access is had to different compounds. For instance,

portions of the tank without removal of the cover.

The loss of sodium hydroxide, or other bath constituent, from-the-fusedbath, due to its being carried away on the surface of the articletreated, may be minimized in various ways as by wiping thewire or otherarticle as it issued from the bath. Sheets, for example, may be passed-between rollers arranged adjacent the exit end of the bath. In theexample shown in Fig. 3 the stream of. steam employed at the exit end ofthe bath acts to blow off considerable vof the sodium hydroxide onthesurface of the wire.

I have already indicated, in my description of the use of a fused bathof sodium hydroxide, that I prefer to operate the bath under suchconditions that I obtain the conjoint action of sodium in the nascentstate and sodium dissolved in the sodium hydroxide. The solution of thereducing metal is a highly importantfeature of my inven tion. Aconsequence of its presence is that reduction of oxidesand othercompounds is notlimited to those portions of the article's surface whichare acting efllciently as cathode. For example, the oxides on both sidesof an article are reduced even when but one side of such article acts ascathode. The importance of this action -of the solution of highlyelectro-positive metal is obvious. Many articles to be cleaned are ofsuch shape that it is practically impossible for all parts of theirsurface to act eificiently as cathode surfaces, as, for example,articles of a tubular construction, those which are deeply recessed, andthe like. As a result of the article being surrounded by a solution ofthe reducing metal, all portions of the article's surface can beeffectively treated.

My process is not limited to the treatment of ferrous metals. Articlesofvarious metals may be efficiently cleaned by subjecting them to theaction of metals having a greater affinity for oxygen than the metalbeing treated.

For example, I have effectively cleaned articles of copper, bronze, andnickel-chromium alloys by using them as cathodes in the electrolysis ofa fused bath of sodium hydroxide. It will be readily appreciated'thatthe essential principles of this invention may be applied 'to metalsgenerally, varying, as desired and as special condi-- tions demand, thedetails of the operation.

Various 'modiflcations'in my process are feasi ble. For example, it ispracticable to produce alloy surfaces on an article at the same time itand other reducible it is possible to give copper a zinc-copper alloysurface, by subjecting the copper as cathode to .electrolysis in a fusedbath. of sodium hydroxide in which zinc oxide is dissolved, the coppernot only being cleaned but is treated to reduce oxides the zinc beingdeposited to alloy with the surface of the copper. Similarly, the coppermay be provided with a surface of a copper-tin alloy by subjecting thecopper as cathode to electrolysis in a fused bath of sodium hydroxide inwhich tin oxide has been dissolved. Lead may be deposited upon ferroussurfaces if a leadcompound is present in the fused bath.

My process may be effectively utilized to produce sponge metal. Forexample, my process is very effective in treating all ferrous materialwhich has exceedingly heavy amounts of scale.

When such material is subjected to my operation, as, for. instance; whentreated in a caustic soda bath, as above outlined, the sodium, both inthe nascent form and in solution in the caustic soda, quicklyandthoroughly reduces the. heavy scale to sponge iron. This sponge iron caybe easily removed by well known operations, such as scrap+ ing, and bythe use of water sprays. The sponge iron thus removed is an importantindustrial product and it is frequently economically advantageous toutilize such material where heavily oxidized material is treated on alarge scale.

I have already indicated that the fused bath may be so used as tocombine with its function of cleaning that of effecting the heatingstage of heat treatments, such as annealing. These heat treatments arevarious. Many of them, such as most forms of normalizing include thestep of heating the metal above the "critical temperature". The fusedbath, which is used for cleaning the metal, may well be employed for theheating step of such heat treating operations. If the desiredtemperature is a very high one care should be taken to employ such acompound as will not react with the metal being treated at the elevatedtemperature. For example, I have found that in the combinedheattreatment and cleaning of ferrous articles a mixture of 50%potassium chloride and 50% sodium carbonate may be usedat considerablyhigher temperatures than sodium hydroxide.

Earlier in this specification 1 have referred to the tendency, undercertain conditions, to reoxidation of the article's surface upon issuingfrom the fused bath, and I have set forth various ways to overcome thistendency. A further means of v reducing or overcoming this tendency isto reduce the current density just before the article leaves the bath.For example, if wire. is being treated in a caustic soda bath and acurrent density of- 100 amperes per square foot of cathodesurface isbeing employed to clean the surface, the current density maybe reducedto 10 amperes or less per square foot ,ofcathode surface just before thewire leaves the fused bath. a

Having thus described my invention what-l claim as new and desire tosecure'by Letters Patent is:

1. In a process of treating a metallic article to remove oxides, scaleand the like, the steps of lacing said article in circuit and subjectingit to electrolysis molten'compound of a metal of the group consisting ofthe alkali and alkaline earth metals adapted to be liberated at" thesurface of the cathode in said electrolysis, said molten bath of thecompound being at a temperature below the boiling point of the liberatedmetal and substantially in excess of the fusion point of the molten as asolid cathode in a bath of compound and sufliciently high to dissolvethe surface of said cathode by solution in said bath and free saidsurface of oxides, scale and the like while the article is in the bath,and then delivering the treated article from said molten bath cleared ofsaid oxides, scale and the like.

2. In a process of treating a metallic article to remove surface oxides,scale and the like, the steps of subjecting the article as a solidcathode to electrolysis in a fused bath of a compound of a metal of thegroup consisting of the alkali and alkaline earth-metals maintained at atempera- .ture below the boiling point of said metal and over 20 C,above the fusion point of said compound with a current density and for atime sufficient to effect a substantially complete reduction of surfaceoxides while the article is in the bath, and then delivering the articlefrom said fused bath cleared of said oxides, scale and the like andsubstantially free from macroscopic amounts of a deposit of said metalon its surface.

3. The process of claim 2 in which the fused bath is of a compound ofsodium maintained at a temperature between 350 C. and 750 C.

4. 'The process of cla.m 2 in which a compound of a metal alloyable withthe metal of the article being treated-is dissolved in the fused bath.

5. In a method of treating metal, the steps of subjecting the metal as asolid cathode to electrolysis in a fused bath of a compound of a metalof the group consisting of the alkali and alkaline earth metals adaptedto be liberated at the surface of said cathode, said fused bath beingmaintained at a temperature below the boiling point of the metal of saidcompound and sutliciently high to dissolve the liberated metal in saidbath and to form a solution of said metal in said bath, and continuingsaid treatment with suflicient current density for a time sufficient toclean the treated metal while in said bath'by the combined liberation ofthe metal of the bath at the cathode and the bathing of the cathode insaid solution of said metal in said compound, and delivering saidtreated metal from said bath free of oxides, scale and the like.

6. The method as set forth in claim 5 in which the treated metal isfreed from actively oxidizing material before said metalis brought intothe free atmosphere.

7. The method as set forth in claim 5 in which at least a portion of thefused bath is maintained at a temperature and moisture contentpreventing reoxidation of the surface of the metal being treated.

8. In a method of treating metal having an oxidized surface, the stepsof subjecting the metal as a solid cathode to electrolysis in a fusedbath of .a compound of a metal of the group consisting of the alkali andalkaline earth metals with a current density and for a time suflicientto effect reduction of the oxides on me metal surface and clean themetal while temperature of the fused bath being more than 20 C. abovethe melting point of said compound but below the boiling point of themetal of said compound and below the temperature at which activelyoxidizing materials are formed upon the surface of the metal, and thendelivering the metal from said bath cleared of said oxides.

9. In a method of treating metal having an oxidized surface, the step ofsubjecting the metal as a solid cathode to electrolysis in a fused bathof sodium hydroxide at a temperature more than 20 0. above the meltingpoint of said hydroxide and below the boiling point of sodium and with acurrent density and for a time suflicient to rein said bath, the

duce substantially completely the metal oxides on the metal surface'andclean the metal while the metal is in the bath.

10. In a method of treating metal having an oxidized surface, the stepof subjecting the metal as a solid cathode to electrolysis in a fusedbath of sodium hydroxide at a temperature more than 20 C. above themelting point of said hydroxide and below 550 C. and with a currentdensity and for a time sufficient to reduce substantially completely themetal oxides on the metal surface and clean the metal while the metal isin the bath.

11. In a method of treating metal, the steps of subjecting the metal asa solid cathode to electrolysis in a fused bath of a compound of a metalof the group consisting of the alkali and alkaline earth metals at atemperature below the boiling point of said metal and substantially inexcess of the fusion point of said compound and with a current densityand for a time sufficient to effect a substantially complete reductionof surface oxides while the metal is in the bath, removing the metalfrom the bath with the surface of the metal cleaned of oxides, scale,and the like and free of any macroscopic deposit of the metal of saidcompound, and immediately subjecting the metal to steam.

12. In a process of treating a metallic article having an oxidizedsurface; the steps of subjecting the article as a solid cathode toelectrolysis in a fused bath comprising a compound of a metal of thegroup consisting of the alkali and alkaline earth metals, thetemperature of the bath being such that the metal being liberated in theelemental condition at the cathode surface during electrolysis of thefused bath is dissolved into the bath as fast as it is liberated,continuing said treatment in said bath to effect substantially acomplete reduction of the oxides on the metal surface and clean thearticle while the metal is in the bath, and effecting an agitation of atleast a portion of the bath during electrolysis wher y the surface ofthe article is freed from subst tending to re-oxidize the surface of thearticle.

13. In a process of treating a metallic article, the steps of subjectingthe article as a solid cathode to electrolysis in a fused bath of acompound of a metal of the group consisting of the alkali and alkalineearth metals adapted to be liberated at the cathode surface, said bathhaving a tempera ture below the boiling point of the metal of saidcompound and appreciably more than 20 C. in excess of the melting pointof said fused bath, the metal being liberated in the elemental conditionat the cathode surface during electrolysis of the fused bath and beingdissolved into the bath as fast as it is liberated, and continuing saidtreatment at said temperature and with a current dencity and for a timesufficient to effect a substantially complete reduction of surfaceoxides while the metal is in the bath.

14. The method as set forth in claim 13 in which the article isdelivered from the bath directly into an oxidation preventingatmosphere.

15. The method as set forth in claim 13 in which the temperature of thefused bath at the surface of the artcle is varied during said treatment.

16. The method as set forth in claim 13 in which the temperature of thefused bath at the surface of the article is relatively higher at thebeginning of the treatment and is lowered before the article isdelivered from the bath.

which the article as it is delivered from the fused r v 2,184,457 bathis subjected to treatment in aifluid reducing the .tendency of thesurface to oxidize.

18. The method as set forth in claim 13 in which the article as itisdelivered from the fused bath is subjected to a current of fluiddischarged along the surface of the article as it emerges from the bathand acting to reduce the oxidation at the surface of the material.

19. In a method of treating a metallic article, the steps of subjectingthe article as a solid cathode to electrolysis in a fused bath ofa'compound of a'metal of the group consisting of the alkali and alkalineearth metals at a temperature above 350 C. and below the boiling pointof the metal of said compound and high enough in temperature to effect aheat treatment-of the metal article being treated and with a currentdensity and for a time suflicient to effect a substantially completereduction of surface'oxides while the articleds in the bath.

.20. In a method of treating a metal article, the step of subjecting themetal article as a solid cathode to electrolysis in a fused bath of asodium compound with elemental sodium dissolved in it at a temperatureabove 338 C. and below the boiling point of sodium and with a currentdensity and for a time suflicient to effect a substantially completereduction of surface oxides while the metal is in the bath. u

' 21. The method of claim 20 in which the sodium compound bath is at atemperature of above URLYN'CLIETON T'AmTON.

